The present invention relates to a diaphragm pump integrally including a quick discharge valve unit.
A diaphragm pump is generally used to supply pressurized air to a pressurization target such as a sphygmomanometer. The diaphragm pump is a pump which delivers air to a pressurization target by deforming a diaphragm portion made of an elastic material. A quick discharge valve unit is integrated with a delivery port of the diaphragm pump like this. When the operation of the diaphragm pump is stopped, the quick discharge valve unit discharges pressurized air remaining in a pressurization target within a short time (e.g., Japanese Patent Laid-Open No. 2012-172577 (see patent literature 1)).
FIG. 6 shows an example of the conventional diaphragm pump integrally including the quick discharge valve unit.
A diaphragm pump 100 includes a diaphragm 7 including a plurality of diaphragm portions 71, a partition member 8 formed on the diaphragm 7, and a quick discharge valve unit 2 formed on the partition member 8.
The diaphragm portions 71 of the diaphragm 7 and the partition member 8 form pump chambers 70. By deforming the plurality of diaphragm portions 71 in order, air taken into each pump chamber 70 through a suction passage 82 formed in the partition member 8 is delivered from an output passage 81 to the quick discharge valve unit 2. A suction valve body 75 and delivery valve body 84 are valve bodies for preventing backflows.
The quick discharge valve unit 2 includes a vessel 9 including a lower housing 10 having a supply passage 106 and an upper housing 11 having a discharge passage 111a, and an elastic member 12 which partitions the inner space of the vessel 9 into an input-side space 9a connected to the pump chamber 70 through the supply passage 106 and an output-side space 9b connected to a delivery passage 113a and the discharge passage 111a. The elastic member 12 includes a discharge port valve body 121 which closes the discharge passage 111a when air is supplied to the input-side space 9a through the supply passage 106, and a check valve body 122 which forms, together with a check valve seat 107 formed in the lower housing 10, a check valve for preventing an inflow of air from the output-side space 9b to the input-side space 9a. 
While the diaphragm pump 100 is in operation, air delivered from the output passage 81 formed in the partition member 8 is supplied to the input-side space 9a through the supply passage 106 formed in the lower housing 10, flows to the output-side space 9b through the check valve (107, 122) and a groove connecting hole 108b formed in a projection 108 of the lower housing 10, and is delivered from the delivery passage 113a formed in a projecting cylinder 113 to a pressurization target (not shown).
When the flow rate of air to be supplied to the input-side space 9a is equal to or lower than a given value, the check valve including the check valve body 122 and check valve seat 107 is kept closed, and the air flows to the output-side space 9b through only the connecting hole 108b and is delivered from the delivery passage 113a to the pressurization target (not shown).
On the other hand, when the flow rate of air to be supplied from the pump chamber 70 to the input-side space 9a increases, the air flows to the output-side space 9b through not only the connecting hole 108b but also the check valve including the check valve body 122 and check valve seat 107.
If, however, air to be supplied to the input-side space 9a has a flow rate to such an extent that the air starts flowing to the output-side space 9b through the check valve including the check valve body 122 and check valve seat 107, air which flows from the input-side space 9a to the output-side space 9b at the timing at which the check valve including the check valve body 122 and check valve seat 107 opens is added to the air passing through the connecting hole 108b. This increases or decreases the flow rate of air to be delivered from the delivery passage 113a to a pressurization target. If the flow rate of air to be delivered to the pressurization target decreases, therefore, pressurization to the pressurization target becomes unstable.